1. Technical Field of the Invention
The present invention relates to the field of broadcast transmissions, such as terrestrial analog or digital TeleVision (TV). In particular, the invention relates to the monitoring of signals in broadcast transmissions.
2. Description of Related Art
In broadcast transmissions like terrestrial analog or digital TV, television sets are adapted to receive TV signals broadcast by transmission centers or stations; for example, a TV signal of a certain broadcaster can be broadcasted through a certain geographic area by means of one or more transmitting antennas, and can be received by television sets, connected to proper receiving antennas, located in the area of broadcasting. The geographic area wherein a certain TV signal can be received is also referred to as being “covered” by the signal.
The features of a TV signal perceived at a particular location within the area of broadcasting depends on several factors.
For example, the strength of the TV signal in a certain location depends on the distance from the antenna irradiating the signal. In addition, the quality of the TV signal may be worsened by possible malfunctioning of the transmission centers, for example due to an uncorrected set up of operation parameters thereof. The quality of the TV signal is also conditioned by the atmospheric conditions in the area of broadcast, e.g., by the presence of rain, snow or fog. A further cause of TV signal degrade is the interference due to the presence of electromagnetic noise sources, like for example other transmission stations broadcasting different TV signals (either licensed or not).
Moreover, the TV signal of a same broadcaster is typically provided within the area of broadcasting by different transmission stations, in different locations and having in general a different irradiating power capability: thus, the signal perceived at a certain location of the area of broadcasting may differ (e.g., in strength) from the signal perceived at another location.
Before starting transmissions in a geographical area, a preventive planning is usually conducted for determining the best network configuration, for example in terms of best locations for placing the transmission stations, type of antennas to be used, and transmission power thereof.
Software tools are commonly used for simulating the TV signal propagation, so as to determine the coverage of an area of interest, as well as significant signal features, like the strength, at different locations in the area, based on a certain broadcast network configuration.
The deployment of the transmission stations within the area of broadcasting, particularly the locations and the transmission power of the antennas, is thus typically made following the indications of the planning phase.
In operation, the broadcaster may wish to monitor the actual signal coverage within the area of broadcasting (or a region thereof). This is typically done by one or more operators, equipped with portable measurement instruments capable of detecting the level of the TV signals, who move around the area to be monitored. Usually, for saving human time and costs, the measurements are conducted only in zones of the area of broadcasting that are reputed critical, e.g., in locations far away from a transmission station, or in dense urban areas.
An example of a commercially available portable measurement system is the DSS5800 Automatic Drive Test System, by Z Technology, Inc. (described in the web page http://www.ztechnology.com/pr_dss5800-2002.html). In particular, the DSS5800 is a portable terrestrial broadcast measurement system adapted to perform analysis on digital or analog TV signals during a drive test. It is a self contained system, incorporating a laptop Personal Computer (PC) running a dedicated drive test application software, and it is capable of measuring the strength of Radio Frequency (RF) fields and Digital TV (DTV) decoded parameters, with plotting and mapping capabilities, useful for generating signal coverage data including a full set of figure-of-merit parameters for DTV signals, and can plot these signal coverage data over a certain monitored area. The DSS5800 system is made up of a RF measuring hardware, an 8-level Vestigial Sideband modulation (8VSB) decoder, a Global Positioning System (GPS) receiver and a laptop PC. Data are collected by the operator during a socalled “drive test”: the user drives to a predetermined location, makes a selected number of measurements of all the chosen frequencies, and then, having paused the system, moves to a next location of interest, for performing further measurements.
Tektronix, Inc. proposes (see document “Multi-layer Confidence Monitoring in Digital Television Broadcasting”, downloadable from the web site of Tektronix at http://www.tek.com/Measurement/App_Notes/25—15952/eng/25W—15952—0.pdf) a multi-layer monitoring system for analyzing broadcasted DTV signals. Since the transmission in DTV systems occurs by means of sequences of signal processing and data processing steps organized into a layered model (more particularly, including compression, formatting, and distribution layers), different probe types are used within the monitoring system for measuring the transmission quality at different layers. For example, at the formatting layer, typical probes must be capable of monitoring characteristics of the digital video signal and, consequently, they include digital audio monitors, picture quality monitors and probes for detecting audio/video delay. For monitoring at the compression layer, the system includes probes capable of detecting malfunctioning in basic Moving Picture Experts Group (MPEG) processing. At the distribution layer, the monitoring system includes probes capable of monitoring the RF transmissions. The multi-layer monitoring system of Tektronix provides for the installation of monitoring probes at the network operator's points-of-presence, in such a way to be able to monitor RF and MPEG parameters of the transmission station. A solution is proposed for a distributed multi-layer confidence monitoring, wherein layer-specific probes are located at regional distribution centers, and connected, via Internet, to a video network operations center.